The present invention relates to irrigation systems, and more particularly, to rain sensors which interrupt the execution of a watering program by an electronic irrigation controller during periods of rainfall.
In many areas of the world, it is necessary to irrigate crops and landscaping due to inadequate seasonal rainfall. Within the past several decades electronically controlled irrigation systems have come into widespread use. They typically include a micro-processor based irrigation controller which executes a stored watering program for turning on and off valves connected to supply lines equipped with sprinklers. The watering program typically activates various zones during run cycles measured in minutes on selected days of the week. The watering program can be adjusted to accommodate seasonal variations in rainfall. However, due to the unpredictability of weather patterns in general, it is desirable to connect a rain or moisture sensor to an electronic irrigation controller so that the sprinklers will not be turned on while it is raining, and for some time period thereafter before the rainfall has either evaporated or soaked into the ground. By interrupting a watering program of an electronic irrigation controller during, and shortly after, a period of rainfall, both purified and reclaimed water can be conserved thus lessening the demand on purification plants, reservoirs and other artificial delivery systems.
Rain sensors and moisture responsive actuators have been developed for use in connection with electronic irrigation controllers. One type of rain sensor operates in response to the weight of rainfall collected in a receptacle. However, this type of rain sensor is adversely affected by wind conditions and the collection of debris, and is too slow in reactivating the watering program. Its evaporative rate is not adjustable. Subterranean moisture sensors have also been developed for use with irrigation controllers. However, they are expensive, unreliable and subject to breakdowns. Rainfall sensors have also been developed which utilize infrared emitter and detector devices that optically detect the presence of collected rainfall. See for example U.S. Pat. No. 5,836,339 of Klever et al. entitled Raindrop Counter and Control System for Irrigation Control Systems. However, these devices are relatively complex and expensive. Another category of rain sensor which has been widely commercialized under the MINI-CLIK(copyright) trademark utilizes a plurality of stacked discs made of a hygroscopic material. The discs expand in response to contact with rain water to depress a spring biased switch to deactivate the watering program of the electronic irrigation controller. When the rain stops, the hygroscopic discs eventually dry out and contract, thereby releasing the switch to re-activate the watering program. See for example U.S. Pat. No. 3,808,385 of Klinefelter entitled Moisture Responsive Switch Actuator.
While rain sensors utilizing hygroscopic discs have proven to be inexpensive and reliable, their principle drawback is that while accumulating rainfall, the sprinkler system can still be running, giving the perception that water is being wasted or that the rain sensor is broken. In addition, they tend to reset too quickly, even after heavy rainfall.
It is therefore the primary object of the present invention to provide an improved, low-cost, reliable rain sensor for use with irrigation controllers.
In accordance with the present invention a rain sensor for use with an irrigation control system includes a housing and an electric switch mounted within the housing. The switch has a spring biased actuating lever movable between a first position in which the switch is in a first state and a second position in which the switch is in a second state. A first moisture absorptive element is mounted within the housing adjacent a first opening therein for receiving rainfall and rapidly expanding a sufficient amount to move the actuating lever of the switch from its first position to its second position. A second moisture absorptive element is mounted in the housing for receiving rainfall through a second opening in the housing for slowly expanding and maintaining the actuating lever of the switch in its second position after the first moisture absorbing element has dried and contracted.